Cork stoppers have been extensively used for stoppering containers containing food products, more particularly bottles containing drinks, and in particular wine, for many years. Cork, a natural material which constitutes the bark of the cork oak tree Quercus suber, has properties that are particularly advantageous for this purpose, especially properties of impermeability to liquids, lightness and mechanical properties of elasticity, resilience and compressibility.
In the present description, the term “cork stopper” means both stoppers consisting exclusively of cork and stoppers made of a material based on cork, of which cork is a major component.
The use of cork stoppers for stoppering bottles of liquid may occasionally give rise to a negative effect regarding the quality of the liquid stored, in particular when this liquid is wine, more specifically impairments of its odor and/or taste. In the field of oenology, these impairments are commonly referred to by the term “corky flavor”. It has been demonstrated that the corky flavor is mainly due to the presence in the cork constituting the stopper of a contaminating aromatic molecule, 2,4,6-trichloroanisole (TCA), which is released by the stopper and which interacts with the wine to modify its organoleptic properties. This molecule originates from the methylation of chlorophenols, which may be derived from various origins.
A very small content of TCA in the wine suffices for consumers to detect a corky flavor therein: the detection threshold for TCA by the human nose is in fact very low, less than 4 ng/l. It is therefore a major challenge for the wine industry to minimize as much as possible the contamination by TCA of cork stoppers used for stoppering bottles, especially wine bottles.
The prior art has proposed various methods for treating cork, prior to forming it into a stopper, which are directed toward ridding it of its aromatic organic contaminants, especially TCA. However, despite the efforts deployed, it has not been possible hitherto to ensure total decontamination of cork stoppers, in particular with respect to TCA.
It is thus recommended, before using cork stoppers for stoppering bottles for conserving a food liquid, and more particularly wine, to test these stoppers for the presence of 2,4,6-trichloroanisole, and thus to anticipate beforehand the risk of impairment of the quality of the liquid associated with the stoppers. Such an analysis is nowadays considered as essential in controlling the quality of cork stoppers.
The main technique proposed by the prior art for this purpose, and which is the subject of standard ISO 20752 (“cork stoppers—assay of releasable 2,4,6-trichloroanisole (TCA)”), consists in taking, in a batch of stoppers, a sample of stoppers, typically composed of twenty stoppers, and in macerating it in a solution simulating wine, more specifically an aqueous-alcoholic solution, so as to simulate the phenomena of migration of TCA that are liable to take place between the cork stoppers and the wine. An aliquot of the macerate thus obtained is sampled via the solid-phase microextraction technique and then analyzed by gas chromatography, with detection by mass spectrometry or electron uptake. Such a method, commonly referred to by the abbreviation SPME, is, however, long to implement. In addition, on account of its destructive nature on stoppers, it can only be performed on a limited number of stoppers from a given batch of stoppers. It therefore gives only a globalized result about the contamination of the batch, and does not at all guarantee that each individual stopper of the batch of stoppers is free from contamination with 2,4,6-trichloroanisole.
A process was moreover proposed in the publication by Lorenzo et al. (2006) Journal of Chromatography, 114: 250-254, for the analysis of a cork stopper for the presence of haloanisoles, especially 2,4,6-trichloroanisole, via successive steps of: heating the stopper in a flask in which is also placed, above the stopper, a bar coated with a layer of polydimethylsiloxane (PDMS); absorption onto this bar of the vapors of certain volatile chemical compounds escaping from the stopper during heating; thermal desorption of these chemical compounds; analysis of these compounds by gas chromatography coupled to mass spectrometry. Such a process however proves to be complex, long and expensive to implement. Moreover, it does not make it possible to obtain reliable results regarding the amount of haloanisoles initially contained in the stopper, on account of the losses of compounds occurring during the steps of adsorption/desorption on the bar.
The present invention is directed toward overcoming the drawbacks of the methods for analyzing cork stoppers for the presence of 2,4,6-trichloroanisole proposed in the prior art, especially those presented hereinabove, by proposing such a method which allows reliable and sensitive detection of the presence of 2,4,6-trichloroanisole in cork stoppers, and, where appropriate, the assay thereof, while at the same time being non-destructive, i.e. it does not impair the chemical, physical or organoleptic properties of the cork, and as such is able to be performed on each individual stopper of a batch of stoppers, ensuring that this stopper remains usable for the subsequent stoppering of bottles, especially wine bottles. The invention is also directed toward ensuring that this process can be totally, or at least partially, automated, easily, quickly and at reduced cost.